1. Field of the Invention
The present invention relates to a transmit-receive front end, and more particularly, to a transmit-receive (TR) front end utilizing a single-ended low-noise amplifier (LNA) and not utilizing a transformer to eliminate signal loss of the LNA due to a transformer, and utilizing asymmetric 2 series switches in the LNA side, to enhance isolation from the power amplifier (PA) to the LNA during a transmission interval and eliminate power loss of the PA due to a TR switch.
2. Description of the Prior Art
Conventionally, a transmit-receive (TR) front end adopts many off-chip components, e.g. a transmit/receive switch, matching networks, transformers, and utilizes separate pins and matching networks for a differential low-noise amplifier (LNA) of a reception (Rx) side and a power amplifier (PA) of a transmission (Tx) side, which requires more cost and larger size on a printed circuit board (PCB).
For example, please refer to FIG. 1, which is a schematic diagram of a conventional TR front end 10. The TR front end 10 includes a LNA 100, a PA 102, separate transformers 104, 106, separate matching networks 108, 110, and a TR switch 112 coupled to an antenna 114. The LNA 110 is fully differential input and output for on-chip noise rejection. The PA 102 is also fully differential to increase the output voltage swing headroom by 6 dB theoretically. As a result, the transformers 104, 106 are required to convert single-ended antenna interfaces to differential circuit interfaces for the LNA 110 and the PA 102, respectively. Except for the LNA 100 and the PA 102, other front-end devices are off-chip components which occupy lots of PCB board area, i.e. the transformers 104, 106, the matching networks 108, 110, the TR switch 112 and the antenna 114. In general, the matching networks 108, 110 at TX and Rx are required to optimize the noise matching and power matching for the LNA 110 and the PA 102 respectively.
In operations of a wireless transceiver, different time intervals are used for transmission and reception. The function of the TR switch 112 during transmit intervals is to couple maximum power from the PA 102 to the antenna 114 and to prevent transmit signals from damaging an input of the LNA 100. On the other hand, the function of the TR switch 112 during receive intervals is to maximize signals from the antenna 114 to the input of the LNA 100 and minimize loss due to a loading effect of the PA 102.
However, although the prior art has flexibility to use high quality off-chip component to optimize transmission and reception performance separately, since there are many off-chip components, more cost and larger size are required on the PCB board. On the other hand, if the prior art directly replaces those off-chip components with on-chip components, large insertion loss may occur, which sacrifices the RF performance. Thus, there is a need for improvement over the prior art.